Attachment 2 - Geotechnical Stability Assessment

                  Roughness                        Investigation Methods
POL                Polished
RJ                 Rough                           Test Pits: These are typically undertaken with a
S                  Smooth                          backhoe or a tracked excavator, allowing
SL                 Slickened                       examination of the insitu soils. Limitations of test
VR                 Very Rough
                                                   pits are the problems associated with collapse
                                                   of the pits, disturbance and difficulty of
      Defects                   Type               reinstatement and the consequent effects on
BP                 Bedding Parting                 close-by structures. Care must be taken if
CL                 Cleavage                        construction is to be carried out near test pit
CO                 Contact                         locations to either properly recompact the
CS                 Crushed Seam                    backfill during construction or to design and
CZ                 Crushed Zone
                                                   construct the structure so as not to be
DB                 Drilling Break
                                                   adversely affected by poorly compacted
DK                 Dyke
DL                 Drill Lift                      backfill at the test pit location.
DZ                 Decomposed Zone
FC                 Fracture                        Hand Auger Drilling: A borehole of typical
FL                 Foliation                       diameter of between 50mm to 75mm advance
FZ                 Fracture Zone                   manually operated equipment.         Premature
HB                 Handling Break                  refusal of the hand augers can occur on a
IS                 Infilled Seam                   variety of materials such as fill, gravel, hard
JT                 Joint                           clays and collapse of the borehole (typically in
H                  Schistosity                     non-cohesive soil).
SI                 Sill
SM                 Seam                            Continuous Spiral flight Augers: The borehole is
SS                 Shear Seam                      advanced using 65mm to 100mm diameter
SZ                 Shear Zone
                                                   continuous spiral flight augers, which are
VN                 Vein
                                                   withdrawn at intervals to allow sampling and
VO                 Void
                                                   insitu testing.  Augers of up to 300mm in
Sampling                                           diameter are used to recover larger volumes of
                                                   sample. Samples are returned to the surface
Sampling is undertaken during the fieldwork to     by the flights or may be collected after
allow examination of the soil or rock and to       withdrawal of the auger flights. Samples can
allow laboratory testing to be undertaken.         be disturbed and layers may become mixed.
                                                   Augering below the groundwater table can be
Disturbed samples taken during drilling provide    less reliable than augering above the water
information on plasticity, grain size, colour,     table.
moisture content and minor constituents. Bulk
samples are similar but of greater volume          A Tungsten Carbide (TC) bit for auger drilling
required for some test procedures such as CBR      into rock can be used to indicate rock strength
testing.                                           and continuity by variation in drilling resistance
                                                   and from examination of recovered rock
Undisturbed samples are taken by pushing a         fragments but provides only an indication of
thin-walled sample tube, usually 50mm              the likely rock strength. Where rock strengths
diameter (known as a U50), into the soil and       may have a significant impact on construction
collecting a sample of the soil contained in a     feasibility or costs, then further investigation by
relatively undisturbed state. Such samples yield   means of cored boreholes may be warranted.
information on structure and strength, and are
necessary for laboratory determination of shear    Wash Boring: The borehole is advanced by a
strength and compressibility.       Undisturbed    bit attached to the end of a hollow rod string,
sampling is generally effective only in cohesive   with water being pumped down the drill rods
soils.                                             and returned up the annulus of the borehole,
                                                   carrying the drill cuttings.      Changes in
Details of the type and method of sampling         stratification can be determined from the
used are given on the attached logs.               return, together with information from “feel”
                                                   and rate of penetration.